Vehicles which operate using natural gas are known. Despite the advantages of natural gas over fuels such as gasoline and diesel both with regard to price and environmental compatibility, vehicles operated using natural gas make up only a negligible fraction of the overall number of all registered vehicles. This is due, inter alia, to the fact that there are considerably fewer fuelling stations for natural gas than there are fuelling stations for gasoline and diesel, and the willingness of vehicle owners to convert to natural gas is therefore only very low.
Japanese Patent Publication JP 2002 257618 A discloses a tank that can be filled with a natural gas such as compressed natural gas (CNG) or a liquefied gas such as liquefied petroleum gas (LPG). Although the flexibility of a vehicle can be increased in this way, this is based on certain conditions. For example, natural gas is stored at a pressure of approximately 200 bar, whereas liquefied gas is stored at a pressure of approximately 10 to 15 bar. This means that a tank filled with natural gas cannot readily be refilled with liquefied gas. This is possible only when the pressure in the tank has fallen below 10 to 15 bar. As is clearly evident, the flexibility seemingly obtained is thus considerably restricted in practice.
Furthermore, it is known to operate vehicles with natural gas and also gasoline. For this purpose, the stated vehicles have a separate tank of approximately 10 to 15 liters storage capacity. Although it is possible in this way to profit from the very dense fuelling station network for gasoline, it is necessary for this purpose to provide a complete gasoline tank system with separate lines, pumps, etc., which firstly restricts the space availability in the vehicle in question and secondly leads to increased purchase costs of such a vehicle. For this reason, few such vehicles are purchased by potential users.